1. Field of the Invention
This invention relates to a method and apparatus for automatic analysis of the concentration of an individual component of a fluid in a metal depositing bath.
2. Description of the Prior Art
The precise determination of the concentration of individual bath components, particularly in the case of metal-depositing baths, often presents difficulties. Although the material composition of the individual bath is known, the difficulty often arises that the individual components are subjected to great fluctuations in quantity of concentration during the operation of the baths. In the case of baths through which current passes and electrochemical separation of molecules takes place, the baths are warm and the fluid evaporates. Also, the metal concentrations in the baths of this type are dependent upon the quantity of production parts to be coated which are guided through the bath. In the case of gold baths, an attempt is made to keep the gold concentration as close to the nominal value as possible. For the quantitative analysis of gold concentration in a gold bath having other important components such as cobalt, citric acid and organic additions besides the gold in complexed form a colorimetric method of analysis is commonly employed. Such a method is known and includes the use of the dyestuff "Astraviolet", 1-methyl-2-(p-diethylaminostyrene-3,3'dimethylindol) chloride (see Armeanu and Baloui, Anal. Chim. Acta, volume 44, [1969] pages 230 to 232).
A quantity such a 1 ml of the bath solution is highly dilued in a first step. A measured fractional quantity such a 1 ml is then taken from this highly diluted quantity. To this fractional quantity, the Astraviolet, as well as a solvent, such as benzene is added. This solution is then intensively stirred. After a rest period, the phases separate into a heavier water phase and a lighter benzene-Astraviolet-gold phase. It is understood, of course, that the solvent as well as the Astraviolet must be in a specific ratio within the diluted bath fluid so that a precise assessment as to the concentration of the gold contained in the solution is possible during the subsequent colorimetric measurement and interpolation with the aid of a calibration curve.
Instead of Astraviolet, a different reagent such as Malachite green may be used. See the Roumanian Review of Chemistry (1968), vol. 13, pages 1617 to 1621. There, the procedure is similar to that the described above and the extraction solvent used may be ethyl ether or carbon tetrachloride.
The aforementioned methods are well suited for determining the gold content. However, these methods are disadvantageous since they can be carried out only with a considerable expenditure of time and only by highly qualified personnel. In the case of high precision baths, it is desireable to carry out the analyses as often as possible in order to rapidly determine concentration deviations of individual components of the bath fluid from nominal values so that, i.e., the bath can again be revived or corrected by the addition of measured quantities of correction fluid. In the case of gold baths, rapid measurements permit uniform quality of coated parts while minimizing the consumption of precious metal.